Circuits are used to drive a load by supplying a potential across the load. Many loads are driven with alternating current in order to modulate the power delivered to the load. Power inverters are often used to generate such alternating current. One type of power inverter is the full bridge circuit. Some full bridge circuits use fast-switching transistors in order to produce alternating current of high frequency.
One type of load that can be driven by a full bridge power inverter is a fluorescent lamp. Compared to incandescent lamps, fluorescent lamps are more efficient and emit less heat. Thus, fluorescent lamps may be more useful in situations in which batteries are being used to power the lamp. Fluorescent lamps that can be driven by such a power inverter include by way of example but not limitation the cold cathode fluorescent lamp (CCFL), the external electrode fluorescent lamp (EEFL), the flat fluorescent lamp (FFL), and other fluorescent lamps. The power inverter may also be used to drive banks of lamps.
CCFLs are commonly used in notebook computers as a backlight for a liquid crystal display (LCD). Portable notebook computer systems, for example, place increasing demands on higher efficiency, smaller size, lower costs, and increased battery life. A critical system that affects this is the power required by the display system. CCFLs are often used in such a display system because CCFLs are efficient and have a low heat emission, rugged electronics, and a long service life. Furthermore, CCFLs, and fluorescent lamps in general, emit light over a broad area and may contribute to even brightness across a notebook computer display screen. Driving a fluorescent lamp differentially (e.g., at both ends) can further improve evenness in brightness.
Today most of the CCFLs used in notebook computers are driven by a full bridge power supply that drives a magnetic step up transformer to apply the high voltage required by the CCFL. In this manner a notebook supply with a typical voltage of 7 to 22 V can tightly regulate a 600 VRMS voltage to the CCFL in an efficient manner. Full bridge power supplies in this application are typically made up of switches connected to one another and to other components of the circuit by bond wires. Parasitic losses occur in the bond wires and switches due to their resistance. Battery life in notebook computers can be prolonged by a reduction of these parasitic losses.
MP1010, MP1011, and MP1015 are manufactured by Monolithic Power Systems. These may be the only commercially available CCFL drivers that integrate the power transistors and control circuitry as of the filing date of this application.